It is known to provide integrated circuit chips for low-speed optical data links, such as in hand-held remote control units for video cassette recorders and similar appliances, and in toy ray guns used in tag games. Typically, these known data links are key pad encoders driving a light emitting diode directly, and processing light from the diode at the receiving end by an integrated circuit chip having a 40 Kilohertz carrier frequency and about a 2 or 3 Kilohertz modulated data rate at the most.
There is a need, however, for bidirectional optical data links between computers and for use with automotive test stands, hand-held data terminals, and the like. These links must, in addition to having a simultaneous bidirectional capability, operate at very high frequencies with a resulting data rate for greater than those obtained by known data links.
IBM Technical Disclosure Bulletin, Vol. 20, No. 7, December 1977, in the name of Closs et al., entitled "WIRELESS CONNECTION BETWEEN A CONTROLLER AND A PLURALITY OF TERMINALS", discloses a system wherein infrared signal transmission is used for connecting a controller with a plurality of terminals in a single room. A downlink from controller to terminals is established by irradiating the room ceiling with an array of LEDs or lasers located in the controller. The diffusely reflected signal is then detected by the receivers in the terminals. An uplink from the terminals to the controller is similar where each terminal has its own array of light emitting diodes but operating on a different infrared wavelength to avoid channel interference in the case of baseband transmission. The two wavelengths are separated by an optical interference filter. As an alternative, the two channels may be separated by different carrier frequencies.
U.S. Pat. No. 4,398,515, issued in 1983, to de Neumann, entitled "PROCESSOR ARRANGEMENT", discloses a number of individual autonomous processor units wherein data communication between the individual processors takes place by means of radiated electromagnetic waves. All of the processors obtain the energy needed to operate them from a common emissive source. The information which the processor receives is obtained via an optical device and an associated receiver. Photodiodes are used and are arranged to operate in the appropriate part of the spectrum, and if required, would be infrared diodes.
The operation of the processors is synchronized by modulating the light emitted by the light source with a synchronization clock signal.
The device of U.S. Pat. No. 4,393,515, however, allocates a particular time slot for data transmission, and does not allow for simultaneous two-way communication over a link.
U.S. Pat. No. 4,553,267, issued in 1985, to Crimmins, entitled "INFRARED TELEPHONE EXTENSION MODULATION SYSTEM", discloses a portable telephone or other signaling system having a remote unit responsive to operator voice and control signals to modulate infrared emitting diodes. The modulation of the infrared diodes occurs with narrowband FM low duty cycle pulses. A modulated infrared emission is provided for remote signaling used in conjunction with complete network control to provide on-and off-hook control and network dialing functions all from a portable unit.
Again, the arrangement of the above patent fails to provide for simultaneous two-way communication over an optical data link.
U.S. Pat. No. 4,688,037, issued in 1987, to Krieg, entitled "ELECTROMAGNETIC COMMUNICATIONS AND SWITCHING SYSTEM", discloses a system for line-of-sight remote selection actuation of a wide variety of apparatuses. A sight couples the eyes of the operator and an array of control positions. The sight is mounted on the head of the operator and defines a line-of-sight for the operator. A processor is provided for converting the portions of the electromagnetic fields received by receiving antennas into the position orientation of receiving antennas with respect to radiating antennas. Using the sight, the operator selectively points to a desired control position and the processor determined which control position is being selected by determining the position and orientation of the operator's head, and thus the line-of-sight of the operator.
Although, this reference discloses a type of optical data link, it does not disclose a high speed, bidirectional computer interface for portable communication.
U.S. Pat. Nos. 3,867,628 and 3,967,111 issued in 1975 and 1976, respectively, to Brown disclose techniques for receiving pulsed light.
U.S. Pat. No. 3,996,476 issued in 1976 to Lazzara, and U.S. Pat. No. 3,774,039 issued in 1973 to Price disclose photoelectric apparatus capable of detecting reflected light. These assemblies, however, are not intended for use adjacent to an assembly emitting light in the same direction from which light is being received.
The "Optodata" 5200 system manufactured by Scientific Technologies Incorporated permits transmission of data via line-of-sight over an infrared beam to both stationery and moving targets, but requires two separate pairs of units, two at each end, for two-way communication. In addition, the second pair of units in a side-by-side arrangement must use different frequencies than the first pair of units. That is, each of the "Optodata" units, which use only a single frequency as a carrier, must be frequency matched to a paired unit and frequency mismatched to adjacent units.